The present invention relates to a process for separating geometric isomers of azolylmethylcyclopentanol derivatives having fungicidal activity. Fungicidally active azolylmethylcyclopentanol derivatives represented by the formula (I):
wherein, R.sup.1 and R.sup.2 each independently represent a hydrogen atom or an alkyl group; each X represents a halogen atom, an alkyl group, a haloalkyl group, a phenyl group, a cyano group or a nitro group; n is an integer of from 0 to 5; A represents a nitrogen atom or a CH group; and each X may be identical or different when n is an integer of from 2 to 5, exist in two stereoisomeric forms, one of which is a geometric isomer having a hydroxy group and a benzyl group on the same side about the plane of the cyclopentane ring (hereinafter referred to as cis isomer), and the other is a geometric isomer having a hydroxy group and a benzyl group on the opposite side about the plane of the cyclopentane ring (hereinafter referred to as trans isomer). Of these two kinds of isomers, the cis isomer is known to exhibit greater fungicidal activity.
The processes for obtaining the cis isomer, therefore, have been proposed as in the following:
(1) An oxirane derivative in cis form (isomer in which an oxygen atom in the oxirane ring and a benzyl group are placed on the same side about the plane of the cyclopentane ring) of the following formula (A) is separated by silica gel column chromatography, and the separated oxirane derivative in cis form is then converted into an azolylmethylcyclopentanol derivative of the following formula (A-I) (U.S. Pat. No. 4,938,792). ##STR2##
In the formulae above, R.sup.11 and R.sup.12 each independently represent a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group; R.sup.10 represents a halogen atom, a C.sub.1 -C.sub.5 alkyl group or a phenyl group; m is an integer of from 0 to 2; and A represents a nitrogen atom or a CH group; provided that both R.sup.11 and R.sup.12 do not represent a hydrogen atom simultaneously.
(2) A 1,2-diol derivative of the following formula (B) is converted into an azolylmethylcyclopentanol derivative in cis form of the following formula (B-1) (U.S. Pat. No. 5,142,061). ##STR3##
In the formulae above, n is an integer of from 0 to 5; R.sup.3 represents a halogen atom, a nitro group, a cyano group, an alkyl group, a haloalkyl group or a phenyl group; R.sup.4 and R.sup.5 each independently represent a hydrogen atom or an alkyl group; A represents a nitrogen atom or a CH group; and R.sup.6 represents an optionally substituted alkyl or aryl group.
(3) An azolylmethyloxabicyclohexane derivative of the following formula (C) is reduced into an azolylmethylcyclopentanol derivative in cis form of the following formula (C-1) (U.S. Pat. No. 5,225,430). ##STR4##
In the formulae above, R.sup.7 represents a halogen atom, a nitro group, a cyano group, an alkyl group, a haloalkyl group or a phenyl group; R.sup.8 and R.sup.9 each independently represent a hydrogen atom or an alkyl group; n is an integer of from 0 to 5; and A represents a nitrogen atom or a CH group.
There have never been proposed, however, the processes for separating a cis isomer from a mixture of geometric isomers of the azolylmethylcyclopentanol derivative produced according to usual processes.
The present inventors, as a result of continuous and earnest studies, have found that a cis isomer of high purity can be separated from a geometric isomer mixture of the compound of the formula (I) by subjecting the mixture to dehydration under acidic condition. Based on the finding, the present invention has been achieved.